Diffuser swirl eliminator



May 25, 1965 c. w. DEMYAN 3,135,131

DIFFUSER SWIRL ELIMINATOR Filed Dec. 13, 1962 3 Sheets-Sheet 1 INVENTOR W CHARLES w. DEMYAN BY 5M ATTORNEY May 25, 1965 c.w. DEMYAN 3,185,181

DIFFUSER SWIRL ELIMINATOR Filed Dec. 13, 1962' s Sheets-Sheet 2 INVENT OR CHARLES W DEMYAN ATTORNEY C. W. DEMYAN DIFFUSER SWIRL ELIMINATOR May 25, 1.965

5 Sheets-Sheet 3 Filed Dec. 13, 1962 INVENT OR CHARLES W DEMYAN ATTORNEY United States Patent 3,185,181 DIFFUESER SWTRL ELrMiNATOR (Charles W. Demyan, Somerville, NJ, assignor to Research-Cottreil, incl, firidgewater Township, Ni, a corporation of New Jersey Filed Dec. 13, 1%2, Ser. No. 244,302 2 Claims. (Cl. 138-457) This invention relates to means for improving fluid flow characteristics in diffusers and, more particularly, the invention provides means for elimination of swirl in Wideangle divergent, subsonic diffusers.

It is an object of the invention to provide swirl elimination means for subsonic divergent diffusers thereby providing improved fluid flow stability, and improved expansion and static pressure recovery.

A further object is to provide swirl'elimination means which are relatively inexpensive to manufacture, simple to install and effective in operation.

A further object is to provide such a device which may be utilized to eliminate or substantially reduce swirl and improve static pressure recovery in substantially any form of subsonic diffuser.

These and other objects and advantages are provided by means for improving fluid flow characteristics in subsonic diffusers comprising a plurality of flow control vanes mounted in a fluid flow passage with the faces of the vanes positioned in parallel spaced relation to each other and extending in planes parallel to a plane including the longitudinal axis of the fluid flow passage a predetermined distance such that the ratio of the distance to the intervane spacing is substantially equal to the reciprocal of the tangent of the approach angle of the flow of fluid to the faces of the vanes.

The invention will be more fully described and other objects and advantages will become apparent to those skilled in the art from the following detailed description when considered with the accompanying drawings Wherein:

FIGS. 1A, 1B and 1C are sketches illustrating helical flow, characteristics of perfect fluids resulting from vector summation of rotational and translational components of fluid flow;

FIG. 2 is a diagrammatic view of fluid flow in a subsonic wide angle diffuser utilizing swirl eliminators of the invention;

FIG. 3 is a perspective view of a typical wide angle difluser equipped with swirl eliminators;

FIG. 4 is a section through a modified form of wide angle divergent subsonic difluser provided with swirl eliminators;

FIGS. 5A and 5B are sketches illustrating the eflect of changes in diffuser inlet aspect ratio on the velocity approach angle 0 of the fluid flow therethrough; and

FIGS. 6A, 6B, 6C, 6D and 6E illustrate a few typical diffuser installations provided with swirl eliminators constructed in accordance with the teachings of the invention.

In order to improve fluid stability and the expansion of fluid flow in divergent diffuser passages, a study of flow characteristics of fluids in divergent subsonic diffusers was undertaken. These studies showed that fluid swirls are formed when a fluid stream enters a divergent diffuser and the magnitude of the swirls are dependent to a large extent on the geometry of the passage leading to the difluser inlet and on the velocity of the fluid flow in the passage. A gas flow passage having a plurality of turns preceding a diffuser inlet was found to energize and aggravate the swirls at the difiuser inlet and it has been determined that the energization of the swirls at the diituser inlet is caused by fluid flow rolls imparted to the moving gas stream as the gas stream passes through the gas flow 3,185,181 Patented May 25, 1965 passage upstream of the difluser inlet. Such rolls are generally helical in configuration and results from both rotational and translational force components of the generally linearly flowing fluid.

FIG. 1A diagrammatically illustrates fluid motion in a passage and illustrates roll about the center of flow C with the speed of rotation increasing from the center outwardly.

FIG. 1B illustrates a vector component of the longitudinal motion of the fluid through the passage illustrated in FIG. 1A. The resulting vector summation of the rotational force illustrated in FIG. 1A and the longitudinal or translatory component illustrated in FIG. 1B is graphically illustrated in FIG. 1C and has a generally helical configuration. If a selection perpendicular to the illustrated vectors is cut through a particular duct or passage configuration the fluid flow would approach a plane parallel to the plane of the section at an angle to be herein designated 0. The vector system diagrammatically illustrated in FIGS. 1A, 1B and 1C is shown in FIG. 2 in a gas conveying system which includes a gas flow passage 10 and a divergent wide angle subsonic diffuser section 12. Adjacent to the entrance to the diffuser section 12 are illustrated a plurality of planar vane members 14 positioned with their plane surfaces parallel to each other and parallel to a plane including the longitudinal axis of the fluid flow passage it For a predetermined gas velocity, the approach angle of the fluid flow in the passage to the extended surfaces of members 14 is at angle 0 The gas flow while approaching the vanes 14 at an angle 6 leave at an angle tangent to the faces of the vanes 14 as illustrated by directional arrows 16.

Thus, the parallel spaced vanes 14 eliminate swirl in the divergent section 12 by removing a substantial portion of the roll of the fluid in the gas flow passage upstream of the diffuser. The length of the vanes 14 and the spacing of the vanes has been found to be dependent on the configuration of the gas flow passage, the velocity of the gas flow and the approach angle of the flow to planes parallel to the surfaces of the swirl eliminators 14.

Referring to FIG. 3, there is illustrated a diffuser generally designated 2% having an inlet width W and a height D. Within the diffuser inlet section 22 are positioned a plurality of swirl eliminator vanes 14 having a height D. The spacing S between the spaced vanes and the distance L are related to the approach angle of the flow of fluids to the faces of the vanes 14 such that the ratio of the distance L to the intervane spacing S is substantially equal to the reciprocal of the tangent of the approach angle 6 Referring to FIGS. 4, 5A and 513, it will be seen that the velocity approach angle 0 will vary with the diffuser inlet aspect ratio. In PEG. 5A a duct 28 is shown that is square in transverse section; therefore, having an aspect ratio of 1. A fluid roll in such a square duct having a velocity vector V will result in an approach angle 0 whereby if the number of vanes employed in the duct is five in number, a length Y for the vanes would provide for removal of the roll prior to the entry of the gas into the divergent section of the diffuser. In FIG. SE a system is illustrated employing the same number of vanes; therefore, the spacing of the vanes would be increased as the cross s ction of the duct illustrated in FIG. 5B is such that side 32 is three times the side 3%, providing a duct having an aspect ratio of 3. The approach angle, at the same volume of gas flow, would then be 0 and each of the vanes 14 would have a length Y due to the greater roll velocity in the duct having an aspect ratio greater than 1.

The number of straightening vanes is not particularly critical. However, for the same gas volume, a larger number will give preferable results in a duct having a high aspect ratio whereas a lesser number may be employed to give the same effective swirl elimination in a duct having a low aspect ratio.

In general, it has been found that satisfactory results are achieved when the spacing 5 FIG. 4, between the vanes 14,, for a duct having a width 1),; is determined by the relationship: 8,; equals the co-tangent of the approach angle theta divided by the length of the vanes. Therefore, in FIG. 4, if the length of the vanes is b and the approach angle is 6 the spacing 5,; would be the distance b divided by the co-tangent of angle 0 Referring to FIGS. 6A, 6B, 6C, 6D and 6E, a plurality of typical subsonic wide-angle diffusers having divergent portions 30A, B, C, D and E and various shaped inlet passages 32A, 32B, 32C, 32D, and 32E are illustrated as examples of duct forms in which the present invention may be embodied.

In each of the specific embodiments of the invention shown in the drawings, the wirl eliminator vanes 34A, 34B, 34C, and 34E are illustrated as being positioned at the inlet to the diffuser. However, it has been found that the vanes may be installed within the diffuser inlet proper as illustrated at 34D in FIG. 6D without adversely affecting the effectiveness of the vanes in eliminating diffuser swirl.

It will be particularly noted with reference to FIGS. 6A and 6B, wherein the divergent portions 39A and 39B and inlet passages 32A and 32B are illustrated as being the same shape and size, vanes 34A are oriented and positioned parallel to the minor side 35A of the inlet passage and vanes 34B are positioned with their plane surfaces parallel to the major side 3813 of the inlet passage 3213.

In both forms of the invention a substantial portion of the roll of the fiuid in the gas flow passage upstream of the diffuser would be eliminated, as elimination of the roll is independent of the orientation of the vanes within the gas fiow passage as long as the vanes are positioned in parallel spaced relation to each other and extend in planes parallel to a plane including the longitudinal axis of the fluid flow passage.

It will be appreciated, however, that preferably the vanes would be positioned with their extended plane surfaces parallel to the minor side of the inlet duct whereby thinner vanes could be used at the same gas velocity without vane flutter.

From the foregoing description, it will be apparent to those skilled in the art that the present invention fully accomplishes the aims and objects hereinbefore set forth.

I claim:

1. Gas flow control means for a subsonic gas flow passage including a subsonic wide-angle divergent diffuser and an inlet passage therefor, a plurality of planar gas flow control vanes mounted in said inlet passage with the plane faces of the vanes positioned in parallel spaced relationship to each other and extending in planes parallel to a plane including the longitudinal axis of the inlet passage a predetermined distance such that the ratio of said distance to the intervane spacing is substantially equal to the reciprocal of, the tangent of the approach angle of the flow of gas to the faces of the vanes.

2. Gas flow control means for a subsonic gas flow passage including a subsonic wide-angle divergent diffuser and an inlet passage therefor, a plurality of planar gas flow control vanes mounted in said subsonic Wide-angle divergent diffuser adjacent said inlet passage with the plane faces of the vanes positioned in parallel spaced relationship to each other and extending in planes parallel to a plane including the longitudinal axissof the fluid gas flow inlet passage a predetermined distance such that the ratio of said distance to the intervane spacing is substantially equal to the reciprocal of the tangent of the approach angle of the flow of gas to the faces of the vanes.

References (fited by the Examiner UNITED STATES PATENTS 2,182,690 12/39 Cole 98--40 2,788,719 4/53 Bennett 13837X LEWIS I. LENNY, Primary Examiner. 

1. GAS FLOW CONTROL MEANS FOR A SUBSONIC GAS FLOW PASSAGE INCLUDING A SUBSONIC WIDE-ANGLE DIVERGENT DIFFUSER AND AN INLET PASSAGE THEREFOR, A PLURALITY OF PLANAR GAS FLOW CONTROL VANES MOUNTED IN SAID INLET PASSAGE WITH THE PLANE FACES OF THE VANES POSITIONED IN PARALLEL SPACED RELATIONSHIP TO EACH OTHER AND EXTENDING IN PLANES PARALLEL TO A PLANE INCLUDING THE LONGITUDINAL AXIS OF THE INLET PASSAGE A PREDETERMINED DISTANCE SUCH THAT THE RATIO OF SAID DISTANCE TO THE INTERVANE SPACING IS SUBSTANTIALLY EQUAL TO THE RECIPROCAL OF THE TANGENT OF THE APPROACH ANGLE OF THE FLOW OF GAS TO THE FACES OF THE VANES. 